Add end-of-string to regex example

doc/user/permissions.md

@@ -244,7 +244,7 @@ The regex pattern format is Ruby, but it needs to be convertible to JavaScript,
 
 Here are some examples:
 
-- Use `\.internal@domain\.com` to mark email addresses containing ".internal@domain.com" internal.
+- Use `\.internal@domain\.com$` to mark email addresses ending with ".internal@domain.com" internal.
 - Use `^(?:(?!\.ext@domain\.com).)*$\r?` to mark users with email addresses NOT including .ext@domain.com internal.
 
 Please be aware that this regex could lead to a DOS attack, [see](https://en.wikipedia.org/wiki/ReDoS?) ReDos on Wikipedia.